1. Field of the Invention
This invention relates to ultrasonic sealing apparatus and more particularly to ultrasonic sealing apparatus utilized in conjunction with bag-forming, -filling and -sealing apparatus.
2. Description of the Prior Art
In making film bags for packing potato chips and similar snacks, apparatus is frequently employed in which the film in sheet form is supplied with a continuous or intermittent motion to a forming apparatus which forms the sheet film into a tubular shape with either overlapping or fin-type edges. Glue or other adhesive is pre-applied to one edge of the film and the film, after being formed into the tubular shape, is passed through a sealing apparatus in which heat and pressure are applied to the edges to effect sealing thereof.
In one form of such apparatus, a transverse seal is made to close the top of one bag and form the bottom of the succeeding bag. A downward pull is applied to the transversely sealed area and the contacting edge of the tubular film is drawn along a device to heat-seal the edge of the next bag. The formed bag is severed, and the process is then repeated on a continuous basis by the apparatus.
This type of bag-forming and -sealing apparatus has some drawbacks. For example, it requires that adhesive be applied to at least one edge of the film. It has certain limitations as to speed of operation because it is necessary to provide time for the glue to liquefy and set in the sealing apparatus. It is subject to defective seals where there is a break in the line of adhesive, or where an inadequate amount of adhesive is applied, or where the adhesive is applied at an improper distance from the edge of the film. An irreducible minimum width of sealing surface is required to insure full sealing engagement of the adhesive under the variables of manufacturing conditions. Further, such apparatus is subject to problems because of the slip-dwell nature of the operation, these problems being particularly serious with longer bags where more than one dwell period is involved.
Ultrasonic apparatus has been used for bonding various plastic and other materials in a number of applications, and has been employed for forming transverse seals at the bottom and top of bags, but, insofar as the applicants are aware, it has not been employed up to this time for edge sealing in bag-forming, -sealing and -filling apparatus. There are particular problems involved with the use of ultrasonic apparatus in this type of application, particularly to avoid burning through the film rather than sealing and these problems are solved by the apparatus of the present application.
With the apparatus of this invention the need for adhesive is eliminated, a lesser width of fin-type or overlapping edges is required, more consistently satisfactory sealing is achieved, and greater speed of operation is achieved.
Accordingly, it is an object of this invention to provide, in connection with a bag-forming, -filling and -sealing apparatus, an ultrasonic apparatus for effecting the back sealing of a bag made from plastic film or plastic-coated paper or other sealable materials.
It is another object of this invention to provide an ultrasonic sealing apparatus which is coordinated with the bag-forming and -filling operation in a manner which ensures an effective ultrasonic seal.